The correct option is D (b) and (c) above.
The process of climbing a mountain in groups is called trekking. To do that, we need to know how to climb a mountain properly and safely. A trekking coach guides a group of people in climbing a mountain. A rucksack is also needed as it contains all the tools necessary to climb a mountain, like trekking poles, carabiners, food, camping tents, and first-aid kit, etc.
Swimwear is not helpful in climbing a mountain. It is used while swimming.